This invention relates generally to amorphous metals, and, more particularly, to a composite material which utilizes an amorphous metal as the bonding medium.
Certain nonmetallic materials such as cubic boron nitride and boron carbide are very hard, with the necessary abrasion and wear resistance for use in implements used to work other materials. However, such very hard materials often lack ductility and fracture toughness, which are necessary in tools such as bits and cutters. Various approaches have been proposed for utilizing the abrasion and wear resistant of such nonmetallics, while at the same time either avoiding the drawbacks caused by their low ductility, or incorporating the nonmetallic into a material system which otherwise provides fracture toughness and some ductility.
For example, a piece of a nonmetallic may be attached to a substrate, so that the nonmetallic is positioned to perform a cutting or working operation. Diamond coated cutting wheels and sandpaper are examples of this approach. In another approach, small pieces of a very hard nonmetallic may be distributed throughout a ductile matrix, with the matrix acting to bond together the pieces of nonmetallic. The familiar tungsten carbide-cobalt sintered composite material is an example of such a material system. Although these approaches have found utility in many applications, full utilization of the properties of the nonmetallics is limited by the performance of the bonding material which bonds the nonmetallic to the substrate or to the other nonmetallics.
In both of these kinds of materials, where the nonmetallics are bonded to a substrate and where the nonmetallics are embedded in a matrix, the bonding medium is often the weak link in the material system. Where the nonmetallics are attached to a substrate, a weak bonding medium can lead to failure at the bond line, and thence to separation and loss of the hard nonmetallic cutting piece. For the composite material wherein the nonmetallics are distributed in a matrix, wear of the matrix can cause undercutting of individual nonmetallic particles at a wear surface, and thence to separation and loss of the nonmetallics. Moreover, cutting tools using nonmetallics must have satisfactory ductility and fracture toughness to absorb shocks produced during the cutting operation, and the bonding medium or matrix should assist in imparting ductility and fracture toughness to the composite.
In diamond-coated tools and other sandpaper-like structures, the bonding medium is typically an adhesive or other agent which is optimized for bond strength, and does not impart significant fracture toughness to the material. In distributed composite materials, such as the tungsten carbide-cobalt sintered composites, the cobalt matrix binds the hard nonmetallics and does impart some ductility and fracture toughness to the composite. The ductility and fracture toughness of the composite increase with increasing volume fraction of the metallic matrix, but at the same time the wear resistance decreases, so that an engineering compromise is usually made to select an acceptable volume fraction of the softer cobalt matrix. Yet even at its optimum matrix volume fraction, the toughness of tungsten carbide-cobalt is lower than desirable. Further, the bonding medium or matrix materials may be susceptible to severe corrosion or stress-corrosion damage in use.
For many of the nonmetallic materials having important commercial potential, there has been discovered no nonmetallic bonding agent which both has sufficient bond strength and also imparts fracture toughness to the composite. As an example, cubic boron nitride might find many important commercial applications in cutting implements if a satisfactory metallic bonding agent could be found.
Accordingly, there has been a need for an improved technique for utilizing hard nonmetallic materials in tooling applications. More specifically, there has been a need for an improved approach to a composite tool material wherein pieces of hard nonmetallics are joined to substrates or bonded within a composite matrix. Ideally, the bonding medium or matrix would be readily and strongly bonded to the nonmetallic, and in addition would be tough, ductile, strong, corrosion resistant, and have a sufficiently high thermal conductivity to dissipate heat produced during the cutting operation. Such composite materials should be readily fabricated in the solid state from available materials, to avoid the need for expensive processing technologies. Further, the composite should be operable in relation to a wide variety of materials, even those which may be chemically unstable in relation to each other at very high temperatures. The present invention fulfills this need, and further provides related advantages.